1. Field of the Invention
This invention relates to a tripot type constant velocity universal joint, and in particular to a tripot type constant velocity universal joint of the type which uses cylindrical rollers and is suitable for use in an automotive vehicle.
2. Related Background Art
In the prior-art tripot type constant velocity universal joint, the track of one rotary member is a concave cylindrical surface and the periphery of a roller loosely fitted onto the trunnion of the other rotary member and engaged with said track is a convex spherical surface and when the joint rotates under a torque with a joint angle present, an axial force is generated on the joint shaft three times per one full rotation of the joint. This axial force is increased or decreased by the influences of the joint angle, the transmitted torque, etc. when the prior-art tripot type constant velocity universal joint is applied to the axle of an automotive vehicle, particularly a vehicle with highoutput engine, the axial force becomes great. There has also been a problem that when the cycle of generation of such axial force coincides with the natural frequency of the vehicle body, the suspension or the like and an axial force great enough to cause resonance of the vehicle body is generated the vehicle seat occupant feels an unpleasant lateral vibration of the vehicle. This has in turn led to inconvenience in the design of a vehicle in that the joint angle must be limited to a relatively small angle.
In respect of this problem, U.S. Pat. No. 3,818,721 (Japanese Patent Publication No. 92448/1974) bears no description of the function and the effect of positively decreasing the axial force, but discloses a tripot type constant velocity universal joint comprising track surfaces formed with three pairs of parallel planar surfaces, and three driving rollers each fixed for rotation and pivotal movement relative to a trunnion and having a cylindrical surface, and each maintained at a predetermined distance from the rotary shaft of the trunnions. This joint has an advantage in that the contact between the rollers and the track surfaces takes place on the generating lines of the outer peripheries of the rollers and no axial force is generated on the axes of the rollers themselves.
However, in such cylindrical type construction according to the prior art, when the joint rotates with a certain angle, each roller rocks and turns on said driving surface and at this time, the roller is freely pivoted relative to the trunnion. Thus, the direction of rolling movement of the roller relative to said driving surface is not perpendicular to the axis of the trunnion, but is arbitrary. In such case, not only a sliding resistance is produced between the rollers and the driving surface, but also a component of this sliding resistance force in the axial direction of the trunnion acts on the rollers. Consequently, a frictional resistance force produced in the portion which supports this component of force hampers smooth rotation of the rollers. These sliding resistance and frictional resistance forces lead to the generation of the axial force.